Electron beam deflection



May 30, 1961 A, TIRICO ELECTRON BEAM DEFLECTION Original Filed July 10,1952 IN VEN TOR.

United States Patent ELECTRON BEAM DEFLE'CTION Arthur L. Tirico, 138Ridgewood Ave., Glen Ridge, NJ.

Original application July 10, 1952, Ser. No. 298,118, now Patent No.2,785,329, dated Mar. 12, 1957. Divided and this application Mar. 8,1957, Ser. No. 644,801

9 Claims. (Cl. 313-76) This application is a division of my co-pendingapplication Serial No. 298,118 which was filed on July 10, 1952, and isto issue as a U.S. Patent 2,785,329 on March 12, 1957.

This invention relates to multiple beam cathode ray devices and/orsingle beam devices so operated as to constitute the equivalent thereof.More particularly it relates to directional color-television picture andpick-up tubes, such as those described in U.S. Patent 2,581,487, inwhich color-selective cooperation between an electron beam and acolor-image transducing surface depends on the direction of convergenceof the beam onto said surface.

One very serious problem which has been encountered in developingdirectional types of color television transducer tubes has been theattainment of uniformity of convergence of a number of electron beams,or of a single beam operated sequentially as the equivalent thereof,toward all parts of an image transducing surface, e.g., toward all partsof a directional dot-phosphor fluorescent screen. Thus whereas theindividual beams of a three beam directional kinescope (or individualsuccessive bursts of electrons in the single nutating beam of anequivalent kinescope, like that shown in the above-mentioned patent) mayconverge accurately upon a picture-element-size area when they areproceeding toward some central portion of the screen, they may fail todo so when proceeding toward a peripheral portion of the screen such astoward one of the corners of the image area. As a result the videoinformation concerning the respective component-colors of asinglefull-color picture element may reproduced at the locations ofdifierent picture element areas which may actually be dozens ofpicture-element areas apart. The effect which this causes might becompared to what would happen in color-printing (with inks) if thecomponent images were printed on a somewhat elastic paper and if thepaper were slightly and unevenly stretched or, otherwise changed to aslightly different shape, before each additional color was applied toit.

Early in the development of these tubes it was found that one reason fornon-uniformity of convergence is that inasmuch as the image-transducingsurface is flat, rather than spherical, all points thereof are notequidistant from the tubes center (or centeroid) of deflection, and away of compensating for this was quickly devised. This consisted ofproviding of dynamic convergence correction in which focusing is variedin synchronism with scanning. While this was very helpful, it still didnot result in satisfactory uniformity of convergence. Although greatefforts have been made to attain a more complete solution they have beenrather unsatisfactory. They involved resort to complicated devicesadapted to permit extremely painstaking adjustments requiring greatskill and intended to offer a trial-and-error way of eliminating, orcompensating for, myriads of aberrations supposedly randomly occurringin the magnetic fields. Besides often being inefiectual this was not apractical solu- 2,986,667 Patented May 30, 1961 tion because of theexcessively high initial cost of color receivers using the devices andmaintenance needs which cannot be met at all with available personnel.

Accordingly it is an object of this invention to provide devices of thekind in question which inherently have greatly improved uniformity ofconvergence and therefore do not require resort to complicated fieldadjustments thereof.

The attainment of this and other objects has been based on the followingprinciples: (1) that the electron optical requirements for accurate anduniform convergence of one or more directional beams are similar to, buton a dimensionally larger scale than, those for accurate uniform focusfor a single axial beam; (2) that a principal one among theserequirements is that a magnetic deflection yoke have a sutficientlylarge throat to avoid excessively close skirting of its interiorsurfaces by any of the electrons in a convergent cone thereof or any ofthe beams in a convergent bundle thereof, as the case may be; and (3)that in preferred embodiments (but not necessarily) the yoke may beprovided with such a sufficiently large throat with a minimum loss inefliciency if it is formed with a tapered-configuration approximatelyconforming to the intended solid angle of deflection.

It should be borne in mind that even the electrons comprising a singleaxial beam do not constitute a fine pencil-like stream as they passthrough the deflection region. Instead they are quite spread out as aresult of having diverged for a considerable distance after leaving thegun and then converged for only a short distance after focusing. Thusthe beam constitutes a cone of electrons whose dimensionally-finitebase-end occupies the deflection region while its sharp apex is directedat the screen where all of the electrons should pass through a smallcross-over point if sharp focus is to be achieved. Because of the baseof the cone subtending a significant amount of space in the deflectionregion any substantial non-uniformity in the magnetic deflection fluxacross that region will divert some of the electrons more than othersand therefore will prevent them from all meeting at the intended commoncross-over point. Such non-uniformity exists close to the inside of thethroat of the yoke since magnetic field gradients Within a solenoidincrease at increasing rates within successive small increments of spacenearer and nearer to its inside surface, i.e., nearer and nearer to itsactual wires. This is particularly important in the case of directionalcolor transducer tubes wherein the thickness of the entire bundle ofconvergent beams of beam paths is necessarily quite substantial. Howeverthose principles and their relationship do not seem to have beenunderstood or at least, judging by the above-mentioned painstakingexpedients which were resorted to in the past, little use was made ofthem if they were.

In the drawing:

Fig. 1 represents a side view, partially in longitudinal section, of anembodiment of the present invention comprising a directionalcolor-television transducer having a tapered throat neck and a taperedthroat magnetic deflection yoke one half of which is shown in positionon the neck, namely one of the two pairs of coils which are used fordeflecting the beam in rectangularly coordinate directions to produce atelevision picture raster, and with the two coils comprising the otherpair removed to clarify the showing;

Figs. 2 and 3 are transverse sectional views of the embodiment of Fig. 1taken respectively along the lines 2-2 and 13-3 therein; and

Fig. 4 represents a longitudinal sectional view of an alternateembodiment of the present invention.

The apparatus shown in Fig. 1 comprises a three gun wide-angledirectional color kinescope 10 having a gun assembly 11 mounted near theclosed or socket end of f 2,986,667 7 [v p p V f the neck 12 andcarrying on said neck a pair of coils (pair 14) of two pairs thereof(14, 16) which together constitute a tapered throat deflection yoke 18which is shown herein in a dissassembled or exploded condition. Thekinescope shown herein by way of example is of the compositeglass-and-metal type. As such it includes a bulb-portion 20, consistingof a metal cone 22, a frame 23 which comprises an extension of the cone22 and is Welded to the large end thereof, a face plate 24 sealed intothe frame 23, and a glass neck portion 12 sealed to the small end of thecone. This structure is often to be preferred since besides providing amechanically excellent vacuum envelope and offering commercialadvantages such as reduced weight, greater safety, and economy ofmanufacture, it has characteristics which render it capable ofperforming certain desired electrical functions and of assistingcooperating components in performing others.

For example, the metal cone 22, by being conductive, can

function as the final accelerating electrode (or part thereof) and, bybeing para-magnetic can function as a magnetic shield, while the glassneck 12, by having appropriate properties, e.g., by being non-magnetic,can assist the yoke 18 in performing its function. However it is notessential that the kinescope envelope be of any particular type for thepurposes of the present invention so long as it is large enough andappropriately-shaped, to accommodate the solid-angle locus of theintended paths of the convergent group of beams and does not interferewith the mounting and function of a suitable tapered-throat deflectionmeans. Thus, the following are examples of alternative types ofkinescope envelopes with which an external magnetic deflection means canbe used: all glass envelopes or different types of composite envelopesin which, like it, the portion which surrounds the beam deflectionregion has the requisite tapered-throat configuration and is of suchmaterial, or is so arranged, that it does not shortcircuit thedeflection flux or otherwise magnetically shield the beam deflectionregion.

In the present application the tapered-throat portion of the envelope isdeemed to be, and is referred to as, a portion of the envelope neck,e.g., the portion of the neck 12 which in Fig. 1 lies between thereference lines 2--2 and 3-3, and the corresponding portion 28 in theembodiment of Fig. 4.

While glass is the material shown herein for making the tapered-throatneck portions of Figs. 1-3 and 4, it is only because at present glass isaccepted as the preferred and the most practical material for thispurpose and not because there is not other suitable material. As analternative, for example, one may use copper, provided it can besuitably insulated from the cone 22 (to keep the high final anodevoltage away from the yoke 18) or that at least the yoke 18 can besuitably insulated from it. In fact if desired the tapered portion mayeven comprise segments -19 or 19' of low-reluctance para-magneticmaterial to serve as pole pieces for the respective four coils of theyoke, so long as they are separated by gaps or segments of highreluctance to avoid magnetically short-circuiting the deflecting fluxaround the deflection region.

As noted above the throat of the yoke 18 should be sufl'iciently largerthan the intended solid angle of deflection 21. so that no beam in theconvergent bundle thereof will so closely skirt the windings of the yokenear its inside surface as to impart substantially more deflection to itthan to any other.

Since the actual spacing in any single case will depend on a pluralityof factors such as the amount of convergence to be employed; the focallength of the tube, the size of the emissive cathode area(s),'thedistance between the focusing electron optic and the deflection yoke,the velocity of the beam electrons, the average flux density within theyoke, etc., it is inadvisable to relay on mathematical computations fordetermining the minimum and optimum spacings which must be maintainedbetween the inside of the yoke throat and the periphery of the intendedsolid angle of deflection. In preference thereto an empirical procedure,such as the following, may be followed: using any suitable trial yokethe dynamic convergence correction should be adjusted to secure the bestpossible uniformity of convergence; the widths of the side and cornerareas wherein the convergence is still poor should be measured; a scaledrawing made be made to represent the paths of the electrons from thecentroid of deflection to points on the screen at the boundaries of theareas of poor convergence; the distance between these paths may bemeasured in the region of the yoke (wherein 1% to 3 inches at the screenmay correspond to perhaps a very small fraction of an inch); and a newyoke may be made which is larger than the trial one in accordance withthese measurements. Where the trial yoke is of a tapered throatconfiguration conforming to the shape of the intended solid angle ofdeflection, then it would be advisable simply to enlarge all of itsinside dimensions without employing any change in configuration. On theother hand where the trial yoke is one having a cylindrical throat(i.e., one in which the factor of efficiency is being to some extentdisregarded) then it' would be possible either to increase its internaldimensions over all of its length or do so only over the forward end ofits throat thereby employing a change in configuration as well as insize. As a result of this procedure a minimum throat size will beobtained which will in effect afford a substantially uniform deflectionflux across the entire solid angle of deflection. In practicalutilization of this invention this is important since good deflectionefliciency will not be possible if the throat is excessively large. Fromthe foregoing it follows that preferred embodiments of a yoke accordingto the present invention should utilize the tapered-throat type ofconfiguration and should employ dimensions for the tapered throat whichare neither too small nor too large.

If it should happen that a production model yoke, i.e., one which hasalready been designed and built, is a little too small under particularcircumstances in which it is used, its tapered configuration will makeit possible, and in fact easy, to correct for this in a very simplemanner by shimming-back the yoke from the neck as shown at 15 in Fig. 1and inserting a' tubular element 19 inside the rear-end of the yoke toshort-circuit the deflec- 'justments may necessitate slightreadjustments of the input currents fed to the yoke to preserve the sizeof the picture.

Where the tapered throat of a yoke has circular cross sections, i.e.,has the approximately frusto conical shape shown in Fig. 1, the lumpedconductor comprising each coil will beshaped with two nearlystraight'sides30, 30 which diverge from ane another at pointsprogressively further along the yoke in the mean direction of beamtravel, to an extent dependent on the desired steepness of taper, twosubstantially semi-circular ends 32, 34 of different inside diameterscorresponding to the diameters of the end openings of the taperedthroat.

Incidentally if it is desired to have the shape of the deflection regionconform even more closely to that of the solid angle of deflection usedfor television scansion, as contrasted for example to the scansion inpolar coordinates used for radar plan-position indicators, both theenvelope (as in Fig. 4) and the deflection yoke may have their throatsshaped to approximately correspond to a truncated rectangular pyramidrather than'to a frustum.

As indicated above it would not be the best practice or the presentinvention to go to extremes in providing abundant space within thethroat of the deflection means and therefore a tapered throatconfiguration should be used so that this space will be relatively smallin regions where deflection of the beams has not progressed very far. Infact the ideal configuration is one in which the intersection of thesides of the throat with a flat plane passing through the neck axis, ineither of the directions of deflection, will be a line parallel to;spaced away from; and having the same curvature as the trajectory of aperipheral electron moving through the deflection region under themaximum influence of the total deflection forces which are effective indirections parallel to that plane.

The following formulas are of interest in that they mathematicallydescribe the path of an electron in a magnetic field:

2m 1 Dd Dd (2) y=DdH= Where:

v- =anode potential E.M.U. H==themagnetic field in gauss =t)hereciprocal of 1.77 E.M.U. w./g. i.e., a

e constant concerning the electron D=distance to face plate from thecentroid of the deflection system in centimeters d=total effectivelength of the deflection system in centimeters y=the deflection ordisplacement of the beam at the screen from the central axis of thesystem R=the approximate radius of the trajectory From the foregoing itcan be mathematically demonstrated that, as is well knovtm in the art,the path of an electron moving through a magnetic field is along acurved line very closely approximating the closely similar shapes ofeither a parabola or a hyperbola.

Thus a theoretically ideal throat shape, where it is desired to use aneck having circular, rather than rectangular cross sections, issubstantially that of a surface of revolution of a parabola (orhyperbola) about an axis from which it is spaced away at one end by thesmallest diameter of the neck; toward which it is convex; and withrespect to which a tangent to its said end will be parallel.

As a practical matter, however, excellent results may be obtained if thetapered throat is actually frusto-conical or truncated-pyramidal insteadof approximately so. Moreover, since either a parabola or a hyperbolacomprises portions which are respectively: (1) substantially circular;and (2) substantially straight, according to nonrigorous standards whichsuffice for the purposes at hand, a good compromise shape for a taperedthroat is that of a surface of revolution of a line which has a portionwhich is substantially straight and is divergent from the axis ofrevolution and a substantially circular portion as a continuation of thedivergent end of the straight portion. An advantage of using atapered-throat neck such as of either the frusto-conical ortruncated-pyramidal type is'that it will afford accurate centering ofthe yoke on the 'neck, since two such tapered surfaces, when pushedtogether, tend automatically to center with respect to each other, thisbeing true whether or not spacing-shims are used between the yoke andthe neck.

A target assembly 36 is mounted in the large end of the bulb portiondirectly behind the face plate 24. It

ing electrode 40 stretched tautly over the frame 38 in the fashion of adrum head bridging the large picture-area opening surrounded by theframe; a shim-spacer 42 for establishing and maintaining a predeterminedspacing between the front surface of the masking electrode and theluminescent screen of the kinescope; a screen plate 44; and adot-phosphor luminescent screen (not shown) carried on the rear surfaceof the screen plate. The entire assembly 36 is carried on a number oflugs 46 which in turn are welded to the interior surface of the cone 22.As is known such an arrangement offers one of a number of possible waysof affording color-selective cooperation between an electron beam and aluminescent screen in accordance with the direction of convergence ofthe former onto the latter.

Fig. 4 shows a modification which employs a neck 12' whose portion 28,corresponding to the deflection region, is of approximatelytruncated-pyramidal shape.

Of course where the deflection forces are not to be applied through theenvelope walls from elements which are mounted outside thereof theenvelope does not have to have any particular shape in the beamdeflection region so long as it provides enough space to contain thedeflection arrangement. Thus a tapered throat magnetic deflection yokemay be mounted within the envelope and, in such a case, no taperedthroat neck would be necessary.

vWhile they are not shown herein because they do not comprise aninventive feature of the apparatus shown herein and are now known in theart, it is to be understood that a tapered throat yoke such as the yoke18 should preferably be provided with the usual para-magnetic wrappingsand/ or cores to restrict external fringing of the fields which theyproduce when in operation and to low the reluctance of their magneticreturn paths.

The term transducer has been employed herein to indicate that thepresent invention is applicable to multiple beam (or equivalent) pick-uptubes as well as multiple beam (or equivalent) picture tubes.

It is to be understood that while particularly great advantages may begained by using the present invention in directional color televisiontransducers nevertheless very significant advantages can also be gainedby using it in multiple gun cathode ray devices having nondirectionalscreens such as in certain cathode ray oscilloscopes employingconvergently trained guns for presenting a plurality of Wave-forms insuperposed plot on the same coordinate axis.

According to another procedure for empirically ap proximating the amountof increase required for the throat size of an experimental yoke,measurements are is well known, arepresentative example of the bestuni-' formity of convergence obtained in the past under the thenstandard conditions of a tight-fitting yoke on a neck two inches indiameter with a one-eighth inch wall thickness, the percentage inquestion will be 20. If a new yoke is then made with a 20% largerthroat, the result will be a 20% increase in the size of the relativelyuniform density central portion of the magnetic flux field providedwithin the yoke. If the first yoke was of the cylindrical throat typecommonly used in the prior art the increase in size could be limited tothe front end of its throat. In fact it is entirely possible that thewidth of the back end could at the same time be so reduced as to fullycompensate for the loss of efficiency occasioned by the increase in thewidth of its front end.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and

therefore only such limitations should be imposed as are indicated inthe appended claims.

I claim:

1. A cathode ray transducer comprising an envelope including a neckhaving a central axis and a bulb attached to an open forward end of theneck, a source of electrons in said neck near its other end, a focalsurface having an image area in said bulb, means for projectingelectrons from said source toward said area through a deflection regionin the neck along radially-spaced-apart plural beam paths soconvergently that if laterally deflected with suitable uniformitythroughout a predetermined solid angle in said region they willsystematically scan said area over respective terminal portions of saidpaths and said terminal portions of the paths will continuously overlapat some point on the area during the scansion thereof, said neck beingadapted to support on the transducer a deflection yoke comprising anassembly of coils defining the interior surface of a hollow throat whichsurrounds the part of the neck containing said defiection region and theapex of said angle when the yoke is supported on the transducer, saidassembly being adapted to produce in said throat cyclically varyingmagnetic fields having suitable intensities to deflect the electronsthroughout said angle but the inherent characteristic that the fieldswill do so with said suitable uniformity in only a limited centralportion of the space within said throat as measured in transversedirections therein, said central portion being surrounded by an annularperipheral portion wherein the fields will not do so with saiduniformity, said peripheral portion comprising a very substantialpercentage of the volume of said space, said assembly being wide enoughin all of its interior dimensions for the limited central portion of thespace within said throat alone to fully accommodate the apex of theangle and all of its portions forward thereof within said regionprovided the assembly is positioned on the neck with said throatsubstantially symmetrically disposed about said axis thereof, thetransducer being characterized in that said part of the neck hassuitably wide exterior dimensions and an exterior configuration whichsuitably mates with said interior configuration of said throat to aloneposition said assembly substantially symmetrically about said axis whenthe yoke is supported on the transducer.

2; A transducer as in claim 1 wherein at least a forwardmost portion ofsaid hollow throat is progressively wider in the same direction as saidangle to at'least partly conform to the widening shape thereof andflares smoothly-outwardly in a configuration adapted to aid insymmetrically disposing said throat about said axis and said transduceris further characterized in that a forwardmost portion of said part ofthe neck has suitably increasing widths at points progressively nearerto said bulb and a suitable exterior configuration to enable it to matewith theoutwardly-flaring portions of the throat when the yoke ispositioned far enough forward thereon to abut tightly against it.

3. A magnetic deflection yoke for systematically sweeping a beam ofelectrons through a predetermined solid angle comprising: an assembly ofcoils surrounding and defining the interior surfaces of a hollow throatthrough which said electrons move in the use of the yoke, and a quantityof high-permeability low-loss material occupying a plurality of segmentsof peripheral throat space within the yoke each segment lying between adifferent side of the solid angle and a respective portion of saidsurfaces ofthe throat which faces inwardly toward it.

4. A magnetic deflection yoke for systematically sweep- 8 defining theinterior surfaces of a hollow throat through which said electrons movein a given general direction in the use of the yoke, said throat beingof such configuration that its intersections with imaginary transverseplanes at successive positions along a central axis which extendsthrough the yoke in said direction are arcuate where ing a beam ofelectrons through a predetermined solid angle comprising: an assembly ofcoils surrounding and they extend around respective sides of said angle,for example because said intersections are circular, while correspondingintersections of said respective sides of the solid angle with saidplanes are substantially straight; and a quantity of high-permeabilitylow-loss material occupying a plurality of segments of peripheral spacewithin the throat each lying between at least a portion of a respectiveone of the sides of the said solid angle and the succession of arcuateportions of said intersections which extend around it.

5. A yoke as in claim 4 wherein transverse cross sections of said polepieces are arcuate on their sides toward said throat and substantiallystraight on their sides toward the said angle.

6. Apparatus comprising a magnetic yoke for systematically sweeping abeam of electrons through a predetermined solid angle comprising anassembly of coils surrounding and defining the interior surfaces of ahollow throat through which said electrons move in the use of the yoke,a neck portion of the envelope of a cathode ray transducer, the saidneck portion positioned within and extending through said throat, andpole pieces of highpermeability low-loss material associated with saidneck portion each occupying a segment of the space within said throatwhich lies between a portion of the interior surface thereof and arespective side of said angle toward throat and an inner surface whichfaces toward a re.

spective side of said angle, is a portion of the inside of said neck andhas substantially straight transverse cross sections.

8. Apparatus as in claim 6 in which said neck portion,

has at least partially rectangularized cross sections over at least apart of its length within said throat and each of the said pole piecesis located between one of the transversely relatively flat sides of theoutside surface of said part of said neck portion and a correspondingpart of the inwardlyfacing surface of said hollow throat.

9. A deflection yoke for systematically sweeping a beam of electronsthrough a predetermined solid angle, said yoke havinga hollow throatwhich is progressively wider in the direction in which electrons travelthrough it in the use of the yoke whereby it conforms at least partiallyto the trajectories of those of the electrons which are subjected to thegreatest amount of deflection during said use, a tubular magnetic-fluxshort-circuiting element positionable within the smaller end of saidthroat, said element being axially moveable therewithin for effectivelyaxially moving the apex of said solid angle of deflection within thethroat to thereby change the clearance between the outermost portions ofthe solid angle and the inwardlyfacing portions of said hollow throat towhich they are most proximate.

,671 Kratz Jan. 28, 1958 Tirico Mar. 12, 1957

